Self-metering semi-automatic quantitative filtration assembly

ABSTRACT

A semi-automatic quantitative filtration assembly is disclosed having a measuring means to measure and present a known quantity of fluid for filtering and a fluid holding means adjacent to a filter medium. The fluid holding means is adapted to receive and hold excess fluid during filtering and to prevent intermixing with a known quantity of fluid to be presented to filtering. The filtering apparatus is designed to filter a quantitative amount of fluid and receive fluid in the fluid holding tank which is excess sample fluid or fluid unwanted as a result of error or operational failure and which drains to a common vacuum/waste means for filtered fluid. A variety of features are also provided to insure proper operation and minimize operator error.

GOVERNMENT RIGHTS

The government has rights in this invention pursuant to Contract No.F33615-80-C-2071 awarded by the U.S. Air Force.

This is a continuation of co-pending application Ser. No. 556,029 filedon Nov. 29, 1983, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a filtering apparatus designed tosemi-automatically accomplish repetitive quantitative filtration.

BACKGROUND OF THE INVENTION

In current practice, quantitative filtration is usually accomplished bya lab technician using glassware items, tubing, a vacuum pump, tweezers,a ring stand, a pipette, petri dishes, and disposable pipette tips. Thegenerally accepted procedure is as follows: with a special flat-bladedtweezer, a filter is carefully removed from between its protectivesheets. With a special rolling motion, the filter is laid across afritted glass filter stoppered into an Erylenmeyer side-arm vacuumglass. A cylinder with a flared, ground-glass base is carefully set overthe filter and centered. A spring loaded clamp is then squeezed over thefritted glass and flared base of the cylinder to rigidly hold the systemtogether. A sample of oil is taken using a pipette technique andsquirted into the cylinder. Vacuum is applied and the progress of thefiltration is monitored visually by the technician. Disassembly requiresremoval of the spring clamp, followed by carefully lifting the filterand placing it in an individual petri dish. Clean up requires a washbottle and a waste container and sink.

Some attempts have been made to automate the foregoing processes. Seefor example, Nuxhall U.S. Pat. No. 4,020,676. However, Nuxhallrepresents a fairly complicated apparatus and does not provide a simplemeasuring means or an in-process holding tank to collect and holdunwanted fluids. Nuxhall also does not have a cover to prevent fluidintroduction at inappropriate times. The need still exists for a simplesystem designed to minimize operator error and to simplify obtaining thedesired quantity of fluid to be filtered.

SUMMARY OF THE INVENTION

The filtering apparatus of the present invention includes a simplemeasuring means to measure and present a known quantity of fluid forfiltering. The present invention also has an in-process fluid holdingtank adjacent to a filter medium. The in-process fluid holding tank isadapted to receive and hold excess fluid during filtering to prevent theexcess fluid from intermixing with the known quantity of fluid to befiltered. The in-process fluid holding tank receives unwanted fluid as aresult of operator error, e.g., if the operator puts too much fluid intothe filtering apparatus, or operational failure (e.g., if the filterplugs). The holding tank drains into the same vacuum/waste means whichdraws the filtered fluid through the filter medium. The measuring meansis moved into and out of engagement with the filter medium and has anoverflow passage to remove excess fluid from the measuring means forsubsequent delivery into the in-process holding tank. Delivery of fluidfrom the in-process fluid holding tank is controlled by a drain and anoutlet valve.

Mechanical interlock means are incorporated into the filtering apparatusto prevent--in conjunction with a removable cover--the addition of fluidinto the filtering apparatus unless the filtering apparatus is incondition to receive and filter same. Specifically, the filter apparatusincludes a movable measuring tube which moves into engagement with thefilter medium. The mechanical interlock prevents the addition of fluidinto the filtering apparatus unless the measuring tube is in engagementwith the filter medium.

A slidable carrier and a frame for holding the filter medium areprovided to ease handling of the filter medium. The slidable carrier islocked in position during filtering. Additional mechanical interlocksare provided to insure proper location of the filter medium andmeasuring tube and registry of the filter medium on the slidablecarrier.

Additional features of the present invention include coarse metering toinsure sufficient fluid to make up the known quantity of fluid in themeasuring means. A rinse means and rinse cycle are also provided.

Various sensors and microswitches may be used to sense positioning ofthe slidable carrier for motor-driven applications, and for sensing theend of the vacuum cycle during filtering.

The advantages of the present invention are that it automates nearly allof the conventional manual filtration process steps, thereby improvingreproducibility of the results and throughput efficiency. An operatorneed not be versed or skilled in chemical laboratory techniques in orderto obtain good results. Some specific advantages include:

(a) the filtering apparatus is a self-contained unit with all neededitems except prepackaged filters;

(b) the filtering apparatus is compact and takes up less space thanlaboratory apparatus;

(c) no breakable glassware is included;

(d) disposable pipette tips are no longer required;

(e) special laboratory techniques which are eliminated includepipetting, tweezer handling of filters, manual rinse, and manualdetection of filtration completion;

(f) operator involvement is minimized, allowing the operator toaccomplish other tasks during filtration;

(g) throughput efficiency for filtering is faster because the number ofoperator steps is grealy reduced; and

(h) reproducibility of results no longer depends on the skill,consistency, and patience of individual technicians.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent to one skilled in theart upon a consideration of the following description taken inconnection with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of a total system embodying thepresent invention in one form;

FIG. 2 is a front plan view of a filtration assembly according to oneform of the present invention;

FIG. 3 is a side plan view of the filtration assembly of FIG. 2;

FIG. 4 is a schematic front view taken along line 4--4 of FIG. 3, withparts removed for clarity;

FIG. 5 is a top plan schematic view of the control and cam assembly ofthe filtration assembly shown in FIG. 2;

FIG. 6 is a partial, schematic cross section taken along line 6--6 ofFIG. 3;

FIGS. 7A-7B schematically illustrate a mechanical interlock for thecover of the filtration assembly shown in FIG. 2;

FIG. 8 is an enlarged cross section of the moat pin and moat valveemployed in one form of the present invention;

FIG. 9 is a top plan view of the in-process holding tank or moatemployed in the filtration assembly of FIG. 2;

FIG. 10 is a bottom plan view of a slidable carrier and filter mediumframe for the filtration assembly of FIG. 2; and

FIG. 11 is a side plan view of the carrier shown in FIG. 10.

DESCRIPTION OF PREFERRED EMBODIMENT

A total filtration system embodying the present invention in one form isschematically shown in FIG. 1. A quantitative filtration system 10 ofthe present invention is connected to a vacuum system through a firstpassage or means to apply a vacuum 12 leading to a waste fluid holdingtank 14 for filtered fluid. A second passage 16 draws a vacuum from thequantitative filtration assembly 10 through passage 12 and waste holdingtank 14. The vacuum is applied by either a portable vacuum pump 18 orthrough port 20 to an auxiliary vacuum system. A valve 22 is provided toconnect the filter assembly 10 up to either the portable vacuum pump 18or the auxiliary vacuum system through port 20.

A rinse fluid holding tank 24 is connected to the quantitativefiltration system 10 through an injection port 26. The rinse fluidholding tank 24 is pressurized by taking the pressure outlet from thevacuum pump 18 through line 28. A valve 30 is provided in the rinsefluid line 28.

With reference to FIGS. 2-4, the major internal working parts of thequantitative filtration assembly 10 will now be explained. A filterassembly is provided with a filter support 32. The filter support 32 ispreferably a fritted glass material, but may be any other suitablefilter support, such as a wire mesh. The filter support 32 is adapted tosupport a filter medium 34. Depending on the fluid to be filtered, thefilter medium may be any suitable filter medium. In the preferred use ofthe present invention in filtering metallic wear particles from engineoil, an anisotropic filter (i.e., unidirectional) is preferred. Aslidable carrier and frame means for holding the filter medium 34 (notshown in FIG. 4) will be explained in more detail below.

A vacuum is drawn through the filter support 32. The vacuum systemincludes a suction funnel 36 which is connected to the vacuum system andis adapted to draw a vacuum through the filter support 32.

An in-processing fluid holding tank 38 is provided. The in-processingfluid holding tank 38 is adjacent and below the filter support 32 in thepreferred form. The in-process fluid holding tank is adapted to receiveat least a portion of a known quantity of fluid positioned above afilter medium in the event a portion of the known quantity of fluid isunable to pass through the filter medium and must be released. In thismanner, excess sample fluid or fluid unwanted as a result of error oroperational failures can be easily collected and removed. In thepreferred form, the in-process fluid holding tank 38 is a moat whichsurrounds the filter support 32 and is positioned below the filtersupport 32.

Above the filter medium 34 is a measuring means 40. The measuring means40 measures and presents a known quantity of fluid for filtering. In thepreferred form of the present invention, the measuring means 40 is ametering tube. The metering tube 40 has an open end 42 which is adaptedto engage the filter medium 34. A fixed distance above the open end 42of the metering tube 40 is an overflow or outlet passage 44. In thismanner, when the metering tube 40 engages the filter medium 34 a knownvolume exists in the lower end of the metering tube 40 between the end42 and the outlet passage 44. Thus, the metering tube 40 is designed tohold a known quantity of fluid for filtering between the end 42 and theoverflow passage 44. Metering tube 40 is secured into two meteringblocks 46 and 48. The metering blocks 46, 48 together comprise part ofthe means to move the metering tube 40 into and out of engagement withthe filter medium 42. The metering blocks 46, 48 are guided for movementon two guides or shafts 50 and 52. The two metering blocks can also bemade as a unitary member.

The inlet funnel assembly 58 is provided with a slidable cover 62, whichhas a viewing glass 64 in the center thereof. The slidable cover 62pivots or slides on a pin near the perimeter of the inlet funnel 58 soas to allow the addition of fluid into the funnel. The inlet funnelassembly 58 is also provided with an injection port 66 which permits theinjection of rinse fluid into the inlet funnel. The inlet funnel cover62 is also provided with a rinse safety interrupt switch 68 whichautomatically stops the addition of rinse fluid through rinse injectionport 66 if the slidable cover 62 is opened during the rinse cycle of thefiltering apparatus 10. The inlet funnel 58 is also provided with acoarse metering line 69 which will be explained in more detail below.

The outlet passage 44 in the metering tube 40 leads to an overflow tube70 which drains by gravity into moat 38. As shown in FIG. 4, the moat 38is sloped toward an outlet 72 which in turn is controlled by an outletvalve 74. The outlet valve 74 for the moat drain 72 is a normally-openvalve which is closed by moat pin 76 acting against the valve. Theoutlet valve 74 uses a leaf spring to bias the valve to a normally openposition. Moat pin 76 is a spring biased pin secured within the lowermetering block 46. The moat pin 76 travels in conjunction with themetering tube 40.

A breakaway in FIG. 4 shows that the moat pin 76 is spring loaded in thefollowing manner. The lower metering block 46 contains a bore 78therethrough. The bore 78 has a narrow end 80 with an opening only bigenough to allow passage of the pin 76. A collar 82 attached to the moatpin 76 acts against a spring 84. A set screw 86 determines the tensionon the spring at rest. When the moat pin 76 comes in contact with theoutlet valve 74, movement of the metering blocks 46, 48 will tend tomove the moat pin 76 downwardly under pressure against the outlet valve74. Upward movement of the moat pin 76 is resisted by the spring 84,thus biasing the moat pin 76 by spring tension against the outlet valve74.

A part of the means for moving the metering blocks 46, 48 together withthe metering tube 40 into and out of engagement with the filter medium34 will be explained with reference to FIG. 5. An outer knob 90 isconnected to a shaft 92. The shaft 92 is supported for rotation throughopenings in a front support 94 and a second inner support 96. Supports94 and 96 are in turn connected to side frames 98 as seen in FIGS. 2 and3. Secured to the other end of shaft 92 is a cam 100. The cam 100 ismounted eccentrically about shaft 92.

As seen in FIG. 6, cam 100 engages a block 102 which in turn is securedto metering blocks 46, 48. Cam 100 engages a projecting surface 104 fromthe block 102, and cam 100 is biased against said surface 104 by aspring 106. If desirable, blocks 102, 46 and 48 could be a unitarymember so long as member 104 is adjustable to allow tension adjustmentbetween metering tube 40 and filter medium 34.

As is clear from FIGS. 4-6, rotation of knob 90 moves cam 100eccentrically about shaft 92. Rotation of the cam 100 against the block104 attached to metering blocks 46, 48 by means of plate 102, causesmovement of the metering tube into and out of engagement with the filtermedium 34. One advantage of using cam 100 is that knob 90 may be movedin either direction to raise or lower the metering tube 40. Ifdesirable, a mechanical stop can be used limiting rotation of the knob90 in only one direction and through only 180°.

The cam mechanism shown in FIGS. 5 and 6 is one suitable method forraising and lowering the metering tube 40. Other suitable arrangementscould be employed, such as a rack and pinion.

The slidable cover 62 is provided with mechanical interlock which isschematically shown in FIGS. 7A-B. At one edge of the slidable cover 62,a pin 108 is secured thereto. At the lower end of pin 108 is aprojecting flange 110. Secured to the filtration apparatus adjacent theupper metering block 48 is a slotted receptacle 112. FIG. 7Aschematically shows the metering block 48 in its upper position. Whenthe metering block 48 is in its upper position, the slotted receptacle112 receives the projecting flange 110 of the slidable cover 62. Whenthe slidable cover 62 is in place covering the inlet funnel assembly 58and the metering block 48 is in its upper position as shown in FIG. 7A,the mechanical interlock between parts 110 and 112 prevents removal ofthe slidable cover 62. That mechanical interlock prevents theintroduction of fluid when the metering tube 40 is in its upper positionand, thus, not ready to accept addition of sample fluid because tube 40is not engaged with filter medium 34. The pin 108 is provided with aspring 111 and a washer 113. The spring 111 causes the funnel cap toseal with the funnel tight enough to prevent solvent from coming outduring the rinse cycle. The up and down movement of the washer 113provides actuation of switch 68 when the funnel cap is opened. Theupward movement of funnel cap 62 is caused by the lower edge of thefunnel cap moving over a corresponding edge on the funnel.

FIG. 7B shows the metering block 48 in its lower position when meteringtube 40 is adjacent and engaging the filter medium 34. Disengagement ofparts 110 and 112 deactivates the mechanical interlock and permits anoperator to remove the slidable cover 62 to add sample fluid forfiltering.

The operation of the moat pin 76 and the moat outlet valve 74 will bedescribed in more detail in conjunction with FIG. 8, which schematicallyshows the moat pin 76 in its lower position biasing outlet valve 74 toits closed position over drain outlet 72. The lower floor of moat 38slopes toward drain outlet 72. Along one side of the moat 38 a leafspring 114 is attached to the moat outlet valve 74. The leaf spring 114is secured to a support 116 such that without any pressure on outletvalve 74, the leaf spring 114 biases outlet valve 74 away from drain 72.

The outlet drain 72 leads to the suction funnel 36 which is the sameoutlet waste passage for filtered fluid drawn through the filter medium34.

In addition to moat pin 76 serving as a means of closing the moat outletvalve 74, the moat pin 76 also serves to insure that the filter medium34 is properly placed between metering tube 40 and filter support 32before the metering tube 40 is lowered. As shown in FIG. 8, and alsoFIG. 10, a slidable carrier 120 is provided. The slidable carrier 120has grooved side channels for receiving the filter medium 34 mounted ina filter holder or frame 124. For convenience, the filter holder 124 canbe a conventional 35 mm slide holder. A recess or hole 126 is providedin the slidable carrier 120, and it is designed to allow moat pin 76 toregister therewith. Similarly, a recess or notch 128 is provided in oneedge of filter frame 124.

The moat pin 76 helps insure proper placement of the filter medium 34and prevents undesired operation of the filtration assembly. Unless theslidable carrier 120 and the filter frame 124 are in proper registry,the moat pin 76 cannot pass through the opening 126 in the slidablecarrier 120 or the notch 128 in the filter frame 124. If the moat pin 76cannot pass through those recesses 126, 128, the operator will be unableto lower the metering blocks 46 and 48 because the moat pin 76 wllprevent complete lowering of the metering blocks and the metering tube40. If the metering tube 40 and the metering blocks 46, 48 are notlowered into their lowermost position so that metering tube 40 engagesfilter medium 34, the mechanical interlock 110, 112 on the cover 62 willprevent the operator from adding fluid to the inlet funnel 58. Thus, themoat pin 76 is designed to insure in conjunction with the slidablecarrier 120 and the filter frame 124 that the apparatus 10 is ready foroperation and the filter is in place before any fluid is added to thesystem.

FIG. 9 is a top plan view of the moat 38 surrounding the filter support32 and being located below filter support 32. The slidable carrier 120slides along surface 130 above the moat 38. Two sets of rollers 132-3and 134-5 are provided on either side of filter support 32 and spacedabove the surface 130 and from each other by space bars 137, 139. Theslidable carrier 120 slides between the rollers and surface 130. Thepurpose of the rollers 132 and 134 is to serve both as a guide for theslidable carrier and also to prevent vertical movement of the slidablecarrier relative to the filtration assembly. The purpose of the separaterollers 132 and 133 (and also 134-5) provide clearance for the optionalinsertion of thick samples and transport to the analysis area 140.

If desired, the moat is provided with an extension 138. The purpose ofthe extension 138 is to provide a second opening 140 for analysis of anymaterials retained on the filter medium 34. For example, after thefilter medium 34 is removed from the filtering station above filtersupport 32, the slidable carrier 120 can be moved to position the filtermedium 34 over opening 140 for analysis. One type of analysis could bean X-ray analysis of wear metal particles in engine oil.

FIGS. 10 and 11 illustrate the slidable carrier 120 of the presentinvention in more detail. When using an anisotropic filter, the presentinvention can be adapted to insure that the filter medium 34 is placedin its proper orientation in the slidable carrier 120. A blocking screw142 may be positioned in the channel in the slidable carrier 120 forreceiving the filter frame 124. If the filter frame 124 is notched atone corner 144, then the filter frame 124 can only be placed in oneorientation in the slidable carrier 120 which will permit the notch 128in the frame 124 to be in registry with the opening 126 in the slidablecarrier 120. The metering tube 40 cannot be brought into engagement withthe filter medium 34 unless the filter frame 124 containing the filtermedium is properly placed within the slidable carrier 120.

The present invention can also be adapted to prevent inadvertentfiltering when no filter medium is in place. A blocking mechanism 148can be added to the slidable carrier and biased away from a fixed stop150 by a spring 152. The spring 152 and the blocking means 148 should bepositioned so that when the spring is at rest, the blocking means 148covers the recess 126 in slidable carrier 120. If no filter frame 124 ispositioned properly in slidable carrier 120, the blocking means 148would prevent the moat pin 76 from passing through recess 126 andtherefore prevent operation of the apparatus. Thus, filter operation isonly possible when filter frame 124 is properly positioned in slidableframe 120 with the filter frame 124 pushing the blocking means 148 awayfrom its blocking position at recess 126 in slidable carrier 120.

As shown in FIG. 11, the upper surface of slidable carrier 120 may beprovided with a gear rack 154. The gear rack 154 is designed to engage apinion gear attached to motor 156. Thus, if motorized movement of theslide 120 is desired, the motor 156 and the gear rack 154 may beutilized. If manual operation of the slidable carrier 120 is desired,scribes on the upper surface of carrier 120 can be provided to markproper positioning of the carrier relative to the filtration assemblyframe.

The operating sequence of the filtration assembly 10 of the presentinvention will now be described. The slidable carrier 120 is removedfrom the filtration assembly, and the filter frame 124 with a properlymounted filter medium 34 is inserted into the carrier 120. Ifanisotropic filters are used, the proper orientation of the filter mustbe achieved. Blocking means 148 will prevent operation of the apparatusunless a filter frame 124 is properly placed in the frame 120. Blockingscrew 142 will insure proper orientation of an anisotropic filter. Whenthe metering blocks 46, 48 are in their upper position, the slidableframe 120 with the properly oriented filter medium 34 is placedunderneath rollers 132, 134 into the apparatus 10 until opening 126 ispositioned over outlet valve 74. Proper registry between the notch 128in the filter frame 124 and the outlet valve 74 with moat pin 76 isnecessary before the metering tube 40 can be lowered. While the meteringblocks 46, 48 are in their raised position, the mechanical interlock110, 112 prevents removal of the slidable cover 62 and thereforeaddition of any fluid into the apparatus. When the slidable carrier 120is properly positioned, the knob 90 can be rotated to lower the meteringblocks 46, 48 and tube 40 so that metering tube 40 engages the filtermedium 34. When the metering tube is properly engaged with the filtermedium, the slidable cover 62 can be removed.

The present invention is designed to insure adequate addition of sampleto provide sufficient fluid for measuring a known quantity of fluid inthe lower end of metering tube 40. Coarse metering is provided by thescribe 69 in inlet funnel 58 and the structure of inlet funnel 58.Accurate and reproducible coarse metering occurs provided that thefilter is sufficiently impermeable so that negligible filtration occursduring coarse and final metering. This is easily accomplished in mostcases as long as no vacuum is applied. Coarse metering is obtained bypouring sufficient sample in the inlet funnel 58 until it reaches thescribe 69. The length and the shape of the outlet 56 of the inlet funnel58 are adjusted to slow delivery of the liquid to the metering tube 40.With suitable adjustments of the scribe 69 and the structure of theinlet funnel for the viscosity of various fluids, it is possible toobtain predictable coarse metering. Coarse metering also tends to beself-compensating: if a person pours fast, the person tends to fillsomewhat above the scribe 69 before stopping; if a person pours slowly,a certain portion of the liquid will already have passed through theinlet funnel. Coarse metering has found to be accurate and reproducibleand permits conservation of sample fluid while assuring a sufficientsupply for the final metering at the lower end of the metering tube 40.

The final metering at the lower end of metering tube 40 is accomplishedby allowing the sample fluid to fill the known volume between the openend 42 of the metering tube 40 and the outlet passage 44. Any fluid inexcess of the known quantity of fluid to be filtered flows out passage44 through overflow passage 70 into moat 38. At that point, moat pin 76has closed outlet valve 74 and the excess fluid is retained in the moat38 and not intermixed with the sample fluid.

The inlet cover 62 is closed and the vacuum is applied to the system. Asthe vacuum is applied to the suction funnel 36, filtered fluid is drawnthrough the filter support 32 into waste line 12 and into a wasteholding tank 14. A vacuum transducer 160 (FIG. 1) on waste holding tank14 can be provided to sense an increase in pressure and thus anindication that the known quantity of fluid in metering tube 40 haspassed through the filter. The vacuum transducer 160 can be designed toautomatically shut off the vacuum system indicating completion offiltration.

After the completion of filtration, the rinse cycle commences. Rinsefluid is inroduced from rinse fluid holding tank 24 through injectionport 66 into inlet funnel 58. The round inlet funnel 58 in conjunctionwith the angle injection port 66 produces a swirling rinse to completelyrinse out the apparatus and insure that residual sample fluid of theknown quantity of fluid on the walls of metering tube 40 is passedthrough the filter medium 34.

At the completion of the rinse cycle, the metering blocks 46, 48 can beraised. Raising the metering blocks in turn raises the moat pin 76 whichallows any excess fluid in the moat 38 to drain into the same suctionfunnel and waste line as the filtered fluid.

The in-process holding tank or moat 38 of the present invention servesseveral purposes. First, it serves to hold any excess sample fluidflowing out of the overflow passage from the metering tube 40, and itprevents the excess fluid from intermixing with the known quantity offluid to be filtered. Second, the moat 38 is designed to receive anyfluid that spills as a result of operator error or operational failure.Third, the moat 38 is designed to receive fluid in the event the filtermedium 34 becomes plugged and filtration cannot be completed. In thatevent, the metering tube 40 would have to be raised even though aquantity of fluid still remains in the lower end thereof. When themetering tube is raised, any remaining fluid in metering tube 40 simplyflows into the moat 38. Another feature of the moat 38 is that the fluidtherein drains into the same waste system using the same line and vacuumsystem as the fluid filtered through the filter medium 34.

During the solvent rinse, it is possible to slide the cover 62 off ofthe inlet funnel 58 because of disengagement of the mechanical interlock110, 112. In that event, a rinse safety interrupt switch 68 may beprovided to shut off the flow of rinse fluid.

Another feature of the present invention is that, during the filteringcycle, movement of the filter medium 34 is minimized. The rollers132-135 prevent vertical movement of the filter medium 34 relative tothe filter support 32 and the metering tube 40. The moat pin 76--as aresult of its engagement in opening 126 in slidable carrier120--prevents linear movement of the slidable carrier 120.

Another feature of the present invention is that a filter frame 124 isprovided to minimize handling of the filter paper. Many filter media orpapers are very fragile and utilization of a filter frame 124 minimizesdamage and contamination of the filter medium during handling. Framedfilters may also be easily stored for future reference and cataloging.

Another feature of the present invention is the structure of theslidable inlet cover 62. The purpose of the slidable cover 62 isthreefold: First, during the rinse cycle, rinse fluid is pumped throughthe angled injection port 66 up against the cover to produce adispersion and a swirling action; second, the cover prevents splash-outduring rinse; and third, the inlet cover prevents through the mechanicalinterlock 110, 112, any introduction of sample at an inappropriate time.

The filtration assembly of the present invention can be operated eithermanually or with a motorized drive using the rack and pinion gear shownin FIG. 11. The motor can be electrically interlocked throughmicroswitches to prevent operation of the motor unless the meteringblock is in the upper or clear position. Automatic position monitoringof both the slidable carrier 120 and the metering tube 40 can beachieved by mechanically operated switches or by strategically placedphototransducers. An additional positioning function is served by themoat plug pin 76, which must pass through the recess 126 in the slidablecarrier 120.

What is claimed is:
 1. A filtering apparatus comprising:means forsupporting a filter medium, measuring means to measure and to present aknown quantity of fluid to a filter medium, means to apply a vacuum todraw said known quantity of fluid through a filter medium, said means toapply a vacuum including waste means to receive fluid drawn through afilter medium, a fluid holding means adjacent and below a filter mediumhaving means (i) for receiving and holding fluid in excess of said knownquantity, which excess fluid does not pass through a filter medium and(ii) for receiving at least a portion of said known quantity of fluidpositioned above a filter medium in said measuring means, which saidportion of known quantity of fluid cannot pass through a filter medium,said means for receiving comprising an inlet into said fluid holdingmeans spaced laterally from a filter medium, and outlet means in saidfluid holding means for draining said fluid holding means into saidwaste means.
 2. A filtering apparatus as claimed in claim 1 includingmeans to move said measuring means into and out of engagement with afilter medium, said measuring means having means for releasing any fluidtherein into said fluid holding means when said measuring means is movedout of engagement with a filter medium.
 3. A filtering apparatus asclaimed in claim 2 wherein said measuring means comprises a meteringtube having an open end for engagement with a filter medium and alateral opening in the wall of said metering tube spaced a knowndistance from said end of said tube, a volume contained in said tubebetween said end and said lateral opening constituting a known volumeand receiving said known quantity of fluid for filtering, and saidlateral opening being positioned to receive any excess fluid.
 4. Afiltering apparatus as claimed in claim 2 wherein said measuring meansincludes overflow means to deliver fluid in excess of said knownquantity to said fluid holding means.
 5. A filtering apparatus asclaimed in claim 4 including means to release fluid through an outletvalve in said outlet means when said measuring means is moved out ofengagement with a filter medium, whereby excess fluid in said fluidholding means is transmitted through said outlet valve to said wastemeans.
 6. A filtering apparatus as claimed in claim 5 wherein said fluidholding means comprises a moat surrounding and being below a filtermedium, said overflow means comprises an overflow opening in saidmeasuring means and an overflow tube for delivering fluid in excess ofsaid known quantity to said moat, said outlet means comprising a drainin the bottom surface of said moat, and said outlet valve meanscomprising a moat valve to control passage of fluid into said drain. 7.A filtering apparatus as claimed in claim 4 including coarse meteringmeans connected to said measuring means to insure sufficient fluid toconstitute said known quantity of fluid, said coarse metering meanshaving means to allow sufficient fluid to fill said measuring means andto allow any excess fluid flow into said overflow means and into saidfluid holding tank.
 8. A filtering apparatus as claimed in claim 2including means preventing addition of fluid into said filteringapparatus unless said measuring means is in engagement with a filtermedium.
 9. A filter apparatus as claimed in claim 8 wherein said meanspreventing addition of fluid comprises a cover preventing theintroduction of fluid into said measuring means and a mechanicalinterlock to prevent opening of said cover unless said measuring meansis in engagement with a filter medium.
 10. A filtering apparatus asclaimed in claim 2 wherein said means for supporting a filter mediumcomprises a filter support, a frame and a slidable carrier means forholding said frame, said carrier means including means for laterallymoving said frame and filter medium over said filter support and meansfor positioning a filter medium between said filter support and saidmeasuring means.
 11. A filtering apparatus as claimed in claim 10including means to prevent said slidable carrier from moving duringfiltering.
 12. A filtering apparatus as claimed in claim 11 wherein saidmeans to prevent said slidable carrier from moving during filteringcomprises:a pin to move in conjunction with the movement of saidmeasuring means into and out of engagement with a filter medium, anopening in said slidable carrier for receiving said pin, said pin havingan end for closing said outlet valve means in said fluid holding means,said frame holding a filter medium having a recess therein, said pinbeing mounted to pass through said recess and opening when in registryand to close an outlet valve means in said outlet means when saidmeasuring means engages a filter medium, whereby movement of saidslidable carrier is prevented during filtering.
 13. A filteringapparatus as claimed in claim 12 wherein said slidable carrier hasprevention means covering said opening therein to prevent operation ofsaid filtering apparatus by precluding engagement of the measuring meanswith a filter medium thereby preventing the addition of fluid theretounless a frame with a filter medium is properly positioned in saidslidable carrier.
 14. A filtering apparatus as claimed in claim 2including rinse means for rinsing said filtering apparatus with rinsefluid after said known quantity of fluid is filtered through a filtermedium, said rinse means having means to project fluid to transport anyresidual fluid on a wall of said measuring means to a filter mediumwhile said measuring means is still in engagement with a filter medium.15. A filtering apparatus as claimed in claim 14 including cycle endsensor means for sensing an increase in pressure after said knownquantity of fluid is filtered through a filter medium, said cycle endsensor means shutting off any vacuum means in response to said increasein pressure.
 16. A filtering apparatus as claimed in claim 15 includinga round inlet funnel, a coarse metering means comprising a mark in saidround inlet funnel, said round inlet funnel being connected to saidmeasuring means, a cover for said round inlet funnel, and said rinsemeans including an injection port angled to swirl rinse fluid in saidround inlet funnel and into said measuring means.
 17. A filteringapparatus as claimed in claim 16 wherein said rinse means furtherincludes a rinse fluid holding tank for supplying rinse during a rinsecycle and means for ceasing the flow of rinse fluid if said cover isremoved during a rinse cycle.
 18. A filtering apparatus as claimed inclaim 2 wherein said means to move said measuring means comprises a cam,means to rotate said cam, means attached to said measuring means toengage said cam, and means to bias said cam into engagement with saidmeans attached to said measuring means, said cam being positioned tohold said measuring means in engagement with a filter medium.
 19. Afiltering apparatus as claimed in claim 2 wherein said means forsupporting a filter medium comprises a filter support and a frame in aslidable carrier, means for guiding said carrier, a motor positioned toengage said slidable carrier, said motor having means to laterally movesaid slidable carrier and frame therein into position over said filtersupport and to position a filter medium between said filter support andsaid measuring means.
 20. A filtering apparatus as claimed in claim 2wherein said means for supporting a filter medium comprises a filtersupport, a frame for holding a filter medium and a slidable carriermeans for holding said frame and filter medium therein, said carriermeans having means for moving said frame and filter medium to a firstposition between said filter support and said measuring means and formoving said frame and filter medium to a second position for a secondoperation.
 21. A filtering apparatus comprising:a slidable carrier forholding a filter medium, a filter medium support, a measuring meanshaving an opening for engaging a filter medium, said measuring meanshaving a known volume for receiving and holding a known quantity offluid and having an overflow opening to remove any excess fluid placedin said measuring means, means to move said measuring means into and outof engagement with a filter medium, means to apply a vacuum to saidfilter support, a moat surrounding said filter support and positionedbelow said filter support, said moat being positioned to receive excessfluid from said overflow opening in said measuring means and beingpositioned to receive at least a portion of said known quantity of fluidpositioned above a filter medium in said measuring means in the eventsaid portion of known quantity of fluid is unable to pass through afilter medium and must be released, said moat including an outlet and anoutlet valve to drain any fluid in said moat to said vacuum.
 22. Afiltering apparatus as claimed in claim 21 including means to releasefluid through said outlet valve when said measuring means is moved outof engagement with a filter medium whereby excess fluid in said moat istransmitted through said outlet valve to said vacuum means as waste. 23.A filtering apparatus as claimed in claim 21 including means preventingaddition of fluid into said filtering apparatus unless said measuringmeans is in engagement with a filter medium.
 24. A filtering apparatusas claimed in claim 23 wherein said means preventing addition of fluidcomprises a cover preventing the introduction of fluid into saidmeasuring means and a mechanical interlock to prevent opening of saidcover unless said measuring means is in engagement with a filter medium.25. A filtering apparatus as claimed in claim 21 including means toprevent said slidable carrier from moving during filtering.
 26. Afiltering apparatus as claimed in claim 25 wherein said means to preventsaid slidable carrier from moving during filtering comprises:a pin tomove in conjunction with the movement of said measuring means into andout of engagement with said filter medium, an opening in said slidablecarrier for receiving said pin, said pin having an end for closing saidoutlet valve means in said moat, a frame for holding said filter medium,said frame having a recess therein, said pin being mounted to passthrough said recess and opening when in registry and to close saidoutlet valve means when said measuring means engages said filter medium,whereby movement of said slidable carrier is prevented during filtering.27. A filtering apparatus as claimed in claim 21 including coarsemetering means connected to said measuring means to insure sufficientfluid to constitute said known quantity of fluid, said coarse meteringmeans having means to allow sufficient fluid to fill said measuringmeans and to allow any excess fluid flow into said overflow opening andinto said moat.
 28. A filtering apparatus as claimed in claim 21including rinse means for rinsing said filtering apparatus with rinsefluid after said known quantity of fluid is filtered through a filtermedium, said rinse means having means to project fluid to transport anyresidual fluid on a wall of said measuring means to a filter mediumwhile said measuring means is still in engagement with a filter medium.29. A filtering apparatus as claimed in claim 28 including cycle endsensor means for sensing an increase in pressure after said knownquantity of fluid is filtered through a filter medium, said cycle endsensor means shutting off any vacuum means in response to said increasein pressure.
 30. A filtering apparatus as claimed in claim 29 includinga round inlet funnel, a coarse metering means comprising a mark in saidround inlet funnel, said round inlet funnel being connected to saidmeasuring means, a cover for said round inlet funnel, and said rinsemeans including an injection port angled to swirl rinse fluid in saidround inlet funnel and into said measuring means.
 31. A filteringapparatus as claimed in claim 30 wherein said rinse means furtherincludes a rinse fluid holding tank for supplying rinse fluid during arinse cycle and means for ceasing the flow of rinse fluid if said coveris removed during a rinse cycle.
 32. A filtering apparatus comprising:aslidable carrier having means to hold a filter medium, means to preventsaid slidable carrier from moving during filtering, a filter mediumsupport, a measuring means having an open end for engaging a filtermedium and an overflow passage to remove any excess fluid placed in saidmeasuring means, said measuring means having a known volume forreceiving and holding a known quantity of fluid between said open endwhen in engagement with a filter medium and said overflow passage, meansto move said measuring means into and out of engagement with a filtermedium, means to apply a vacuum to said filter support, said means toapply a vacuum including a waste means to receive fluid drawn throughsaid filter medium, a moat surrounding said filter support andpositioned below said filter support, said moat having means forreceiving excess fluid from said overflow passage in said measuringmeans and for receiving at least a portion of said known quantity offluid positioned above a filter medium in said measuring means in theevent said portion of known quantity of fluid is unable to pass througha filter medium and must be released, said moat including an outlet andan outlet valve to drain any fluid in said moat to said vacuum means,means to release fluid through said outlet valve when said measuringmeans is moved out of engagement with a filter medium whereby excessfluid in said moat is transmitted through said outlet valve to saidvacuum means, an inlet funnel for receiving an input of fluid andtransmit said fluid into said measuring means, a removable cover adaptedto cover an input opening in said inlet funnel, means preventing removalof said cover unless said measuring means is in engagement with a filtermedium, rinse means for rinsing said filtering apparatus with rinsefluid after said known quantity of fluid is filtered through a filtermedium, said rinse means having means to project fluid to transport anyresidual fluid on a wall of said measuring means to a filter mediumwhile said measuring means is still in engagement with a filter medium,and an injection port in said inlet funnel adapted to swirl rinse fluidin said inlet funnel and into said measuring means, whereby saidfiltering apparatus is designed to filter a quantitative amount of fluidand receive fluid in said moat which is excess sample fluid or fluidunwanted as a result of error or operational failure and which drainswaste fluid into said waste means.
 33. A filtering apparatuscomprising:a slidable carrier having means to hold a filter medium, afilter medium support, a measuring means having an opening for engaginga filter medium, said measuring means having a known volume forreceiving and holding a known quantity of fluid and having an overflowopening to remove any excess fluid placed in said measuring means, meansto move said measuring means into and out of engagement with a filtermedium, means to apply a vacuum to said filter support, and meanspreventing addition of fluid into said measuring means unless saidmeasuring means is in engagement with a filter medium, said meanspreventing addition of fluid comprises a removable cover preventing theintroduction of fluid into said measuring means and a mechanicalinterlock to prevent opening of said cover unless said measuring meansis in engagement with said filter medium.
 34. A filtering apparatus asclaimed in claim 33 including:a moat surrounding said filter support andpositioned below said filter support, said moat being positioned toreceive excess fluid from said overflow opening in said measuring meansand being positioned to receive at least a portion of said knownquantity of fluid positioned above a filter medium in said measuringmeans in the event said portion of known quantity of fluid is unable topass through a filter medium and must be released, and said moatincluding an outlet and an outlet valve to drain any fluid in said moatto said vacuum.